fixes #157, renaming local library identifiers if needed.

lib/runtime/dart/_js_helper.js

Index: lib/runtime/dart/_js_helper.js
diff --git a/lib/runtime/dart/_js_helper.js b/lib/runtime/dart/_js_helper.js
index 0c9ebb3da9b2c9fb9c2b737d19b1676b9bba06a9..1f965bb7750f1b376773fe09588ba5fa6363f7f8 100644
--- a/lib/runtime/dart/_js_helper.js
+++ b/lib/runtime/dart/_js_helper.js
@@ -1,5 +1,5 @@
-var _js_helper;
-(function(exports) {
+var _js_helper, core, collection, _internal, _foreign_helper, _js_embedded_names, _interceptors, _js_names, async, _isolate_helper;
+(function(exports, core, collection, _internal, _foreign_helper, _js_embedded_names, _interceptors, _js_names, async, _isolate_helper) {
   'use strict';
   class NoSideEffects extends core.Object {
     NoSideEffects() {
@@ -4080,4 +4080,4 @@ var _js_helper;
   exports.missingMain = missingMain;
   exports.badMain = badMain;
   exports.mainHasTooManyParameters = mainHasTooManyParameters;
-})(_js_helper || (_js_helper = {}));
+})(_js_helper || (_js_helper = {}), core, collection, _internal, _foreign_helper, _js_embedded_names, _interceptors || (_interceptors = {}), _js_names, async, _isolate_helper || (_isolate_helper = {}));